U.S. patent application number 15/180923 was filed with the patent office on 2016-12-22 for base station and method for controlling wireless communication.
The applicant listed for this patent is FUJITSU LIMITED. Invention is credited to Nobukazu FUDABA.
Application Number | 20160373988 15/180923 |
Document ID | / |
Family ID | 57587215 |
Filed Date | 2016-12-22 |
United States Patent
Application |
20160373988 |
Kind Code |
A1 |
FUDABA; Nobukazu |
December 22, 2016 |
BASE STATION AND METHOD FOR CONTROLLING WIRELESS COMMUNICATION
Abstract
A base station including: a processor configured to: form a
plurality of cells, each of the plurality of cells having each of a
plurality of different frequency bands, obtain capability
information and state information when a number of a plurality of
terminals coupling to a specified cell of the plurality of cells
exceeds a predetermined threshold, the capability information
indicating each capability of each of the plurality of terminals
for coupling to a different cell of the plurality of cells, the
state information indicating each state of each coupling between
each of the plurality of terminals and the different cell, select a
first terminal from among the plurality of terminals based on the
first information and the second information, a coupling between
the first terminal and the specified cell being to be released, and
switch a cell coupled by the first terminal, from the specified
cell to the different cell.
Inventors: |
FUDABA; Nobukazu; (Yokohama,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJITSU LIMITED |
Kawasaki-shi |
|
JP |
|
|
Family ID: |
57587215 |
Appl. No.: |
15/180923 |
Filed: |
June 13, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W 36/22 20130101;
H04W 36/0069 20180801 |
International
Class: |
H04W 36/22 20060101
H04W036/22 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 16, 2015 |
JP |
2015-121536 |
Claims
1. A base station comprising: a memory; and a processor coupled to
the memory and configured to: form a plurality of cells, each of
the plurality of cells having each of a plurality of different
frequency bands, obtain capability information and state
information when a number of a plurality of terminals coupling to a
specified cell of the plurality of cells exceeds a predetermined
threshold, the capability information indicating each capability of
each of the plurality of terminals for coupling to a different cell
of the plurality of cells, the state information indicating each
state of each coupling between each of the plurality of terminals
and the different cell, select a first terminal from among the
plurality of terminals based on the first information and the
second information, a coupling between the first terminal and the
specified cell being to be released, and switch a cell coupled by
the first terminal, from the specified cell to the different
cell.
2. The base station according to claim 1, wherein a terminal of the
plurality of terminals, when the terminal has an capability for
coupling to the different cell and a state of coupling between the
terminal and the different cell is better than a predetermined
state, is selected to be the first terminal.
3. The base station according to claim 1, wherein a terminal of the
plurality of terminals, when the terminal does not have an
capability for coupling to the different cell, is not selected to
be the first terminal.
4. The base station according to claim 1, wherein a terminal of the
plurality of terminals, when a state of coupling between the
terminal and the different cell is not better than a predetermined
state, is not selected to be the first terminal.
5. The base station according to claim 1, wherein the first
terminal is one of a terminal of first type and a terminal of
second type and a terminal of third type, the terminal of first
type being a terminal that communicates with the different cell and
the specified cell depending on the different cell in parallel, the
terminal of second type being a terminal that communicates with one
of the different cell and the specified cell, the terminal of third
type being a terminal that communicates with the specified cell and
the different cell depending on the specified cell in parallel.
6. The base station according to claim 1, wherein when the first
terminal is the terminal of first type, the processor is configured
to release a radio resource for the first terminal for coupling to
the different cell.
7. The base station according to claim 1, wherein when the first
terminal is the terminal of second type, the processor is
configured to command the first terminal to perform handover from
the specified cell to the different cell.
8. The base station according to claim 1, wherein when the first
terminal is the terminal of third type, the processor is configured
to release a radio resource for the first terminal for coupling to
the different cell and to switch a radio resource, for the first
terminal for coupling to the specified cell, to the different
cell.
9. The base station according to claim 1, wherein the cell coupled
by the first terminal is switched form the specified cell to the
different cell in order of the first type of terminal, the second
type of terminal and the third type of terminal.
10. The base station according to claim 1, wherein the processor is
further configured to: obtain third information indicating each
received quality of each of the plurality of terminals from another
cell formed by another base station, select, after a cell coupled
by the first terminal is switched from the specified cell to the
different cell and when the number of plurality of terminals
coupling to the specified cell exceeds the predetermined threshold,
a second terminal from among the plurality of terminals coupling to
the specified cell and a plurality of different terminals coupling
to the different cell based on the third information, a coupling
between the second terminal and the specified cell or the different
cell being to be released, and switch a cell coupled by the second
terminal to the another cell.
11. A method for controlling a wireless communication, the method
comprising: forming a plurality of cells, each of the plurality of
cells having each of a plurality of different frequency bands;
obtaining capability information and state information when a
number of a plurality of terminals coupling to a specified cell of
the plurality of cells exceeds a predetermined threshold, the
capability information indicating each capability of each of the
plurality of terminals for coupling to a different cell of the
plurality of cells, the state information indicating each state of
each coupling between each of the plurality of terminals and the
different cell; selecting a first terminal from among the plurality
of terminals based on the first information and the second
information, a coupling between the first terminal and the
specified cell being to be released; and switching a cell coupled
by the first terminal, from the specified cell to the different
cell.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based upon and claims the benefit of
priority of the prior Japanese Patent Application No. 2015-121536,
filed on Jun. 16, 2015, the entire contents of which are
incorporated herein by reference.
FIELD
[0002] The embodiments discussed herein are related to a base
station and a method for controlling a wireless communication.
BACKGROUND
[0003] In recent years, there has been known a base station device
that has a multi-carrier function and that simultaneously manages
multiple cells having different frequency bands and communicates
with the multiple cells or terminals connected (or coupled) to the
multiple cells.
[0004] In the base station device having the multi-carrier
function, when multiple terminals temporarily concentrate into a
specific cell among the multiple cells, the number of terminals
connected to the specific cell may exceed a predetermined
threshold. In this case, it is difficult for the terminals
connected to the specific cell to maintain communication with the
base station device. For example, when the exceeded terminal
wishing to connect to the specific cell poses an interference
problem by starting to connect to the other base station devices,
the communication becomes difficult.
[0005] For solving this problem, for example, when the number of
terminals connected to the specific cell exceeds the predetermined
threshold, it may be considered to perform load balance control to
change a connection destination (or connecting destination) of the
terminal from the specific cell to another cell having a less
number of terminals among the multiple cells.
[0006] However, some of the terminals have no connection capability
(or coupling capability) to the other cell or are poor in the
connection state (or coupling state) with the other cell. Thus, it
may become difficult to change the connection destination of such
terminals to the other cell, and therefore the problem of the
excessive number of users may not be solved by the load balance
control only.
[0007] As a conventional technique, the following technique is
disclosed by Japanese Laid-open Patent Publication Nos. 11-136729
and 2014-236504 for solving the problem of the excessive number of
terminals in the specific cell by methods other than the load
balance control mentioned above. As an exemplary conventional
technique applied to a base station device managing one cell, there
is a technique of a handover of a terminal connected to the cell of
the base station device to an adjacent cell managed by another base
station device while reducing transmission power of the cell of the
base station device.
SUMMARY
[0008] According to an aspect of the invention, a base station
includes a memory, and a processor coupled to the memory and
configured to: form a plurality of cells, each of the plurality of
cells having each of a plurality of different frequency bands,
obtain capability information and state information when a number
of a plurality of terminals coupling to a specified cell of the
plurality of cells exceeds a predetermined threshold, the
capability information indicating each capability of each of the
plurality of terminals for coupling to a different cell of the
plurality of cells, the state information indicating each state of
each coupling between each of the plurality of terminals and the
different cell, select a first terminal from among the plurality of
terminals based on the first information and the second
information, a coupling between the first terminal and the
specified cell being to be released, and switch a cell coupled by
the first terminal, from the specified cell to the different
cell.
[0009] The object and advantages of the invention will be realized
and attained by means of the elements and combinations particularly
pointed out in the claims.
[0010] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory and are not restrictive of the invention, as
claimed.
BRIEF DESCRIPTION OF DRAWINGS
[0011] FIG. 1 is a configuration diagram of a radio communication
system including a base station device according to the
embodiment;
[0012] FIG. 2 is a diagram for illustrating a premise technique for
solving a problem of the excessive number of terminals in a
specific cell;
[0013] FIG. 3 is a block diagram of the base station device
according to the embodiment;
[0014] FIG. 4 is a diagram for illustrating selection of a first
type terminal, a second type terminal or a third type terminal by a
candidate terminal selection unit according to the embodiment;
[0015] FIG. 5 is a diagram for illustrating an example of changing
the connection destination of the first candidate terminal when the
first candidate terminal is the first type terminal;
[0016] FIG. 6 is a diagram for illustrating an example of changing
the connection destination of the first candidate terminal when the
first candidate terminal is the second type terminal;
[0017] FIG. 7 is a diagram for illustrating an example of changing
the connection destination of the first candidate terminal when the
first candidate terminal is the third type terminal;
[0018] FIG. 8 is a diagram for illustrating an example of changing
the connection destination of the second candidate terminal;
[0019] FIG. 9 is a diagram illustrating an example of an internal
table used by the candidate terminal selection unit;
[0020] FIG. 10 is a flowchart of a process of changing the
connection destination of a terminal by the base station device
according to the embodiment;
[0021] FIG. 11 is a flowchart of an in-cell connection destination
changing processing according to the embodiment;
[0022] FIG. 12 is a diagram for illustrating an example of
generating a candidate terminal list;
[0023] FIG. 13 is a flowchart of an out-cell connection destination
changing processing according to the embodiment; and
[0024] FIG. 14 is a diagram illustrating a hardware configuration
example of the base station device.
DESCRIPTION OF EMBODIMENTS
[0025] However, in a case where the base station device is the base
station device having the multi-carrier function, the conventional
technique performs handover of the terminal in the specific cell
having the number of terminals exceeding the threshold to the
adjacent cell and reduces the transmission power of the specific
cell. For this reason, even when the number of terminals connected
to the other cell among the multiple cells in the base station
device is not larger than the threshold, the conventional technique
performs handover from the specific cell to the adjacent cell and
reduces the transmission power. As a result, there is a possibility
that the conventional technique deteriorates the signal quality in
the specific cell.
[0026] In view of the foregoing problems, it is an object of the
present disclosure to provide a base station device and a base
station device control method capable of suppressing deterioration
of the signal quality in the cell of the base station.
[0027] Hereinafter, an embodiment of the base station device and
the base station device control method according to the present
disclosure is described in detail with reference to the
accompanying drawings. Note that the disclosed technique is not
limited by the embodiment.
EMBODIMENT
[0028] FIG. 1 is a configuration diagram of a radio communication
system including a base station device according to the embodiment.
As illustrated in FIG. 1, the radio communication system according
to the embodiment includes a base station device 1 and terminals
2-1 to 2-4.
[0029] The base station device 1 includes a multi-carrier function.
Specifically, the base station device 1 communicates with multiple
cells having different frequency bands or the terminals 2-1 to 2-4
respectively connected to the multiple cells. In the example of
FIG. 1, the base station device 1 communicates with the terminals
2-1, 2-2, and 2-4 connected to a cell C1. Also, the base station
device 1 communicates with the terminal 2-3 connected to a cell C2.
FIG. 1 illustrates an example of the base station device 1 managing
the two cells having different frequency bands. However, the number
of cells managed by the base station device 1 may be three or
more.
[0030] The terminals 2-1 to 2-4 transmit and receive data from the
base station device 1 by using a radio resource of the cell C1 or
C2.
[0031] Here, the number of terminals connectable to the cell C1 or
C2 is limited by a predetermined threshold. When the number of the
terminals connected to the cell C1 or C2 exceeds the predetermined
value, it is difficult for the terminal connected to the cell C1 or
C2 to maintain communication with the base station device 1. For
example, when the exceeded terminal wishing to connect to the cell
C1 or C2 poses an interference problem by start to connect to the
other base station devices, it is difficult for the terminal to
maintain communication with the base station device 1.
[0032] Next, before describing the base station device 1 according
to the embodiment, a technique as a premise for the base station
device 1 is described. FIG. 2 is a diagram for illustrating the
premise technique for solving the problem of the excessive number
of terminals in the specific cell.
[0033] In FIG. 2, both the base station device 1 and a base station
device 3 are base station devices providing the multi-carrier
function to the terminals by using two cells. The base station
device 1 may communicate with up to two terminals in each of the
cells C1 and C2, and the base station device 3 may communicate with
up to two terminals in each of cells C3 and C4. That is, the
connection number threshold indicating the number of the terminals
connectable to each of the cells C1 to C4 is "2". In FIG. 2, f1
indicates a frequency band common to the cells C1 and C3, and f2
indicates a frequency band common to the cells C2 and C4. In FIG.
2, ID is an identifier for identifying a terminal to which the
radio resource is allocated when the base station device 1 or 3
performs scheduling processing, and three IDs are defined for each
cell. In FIG. 2, each of #1 to #4 indicates the radio resource
allocated respectively to the terminals 2-1 to 2-4 in each
cell.
[0034] State (1) of FIG. 2 indicates a state in which the terminal
2-4 is newly connected to the cell C1 while the terminals 2-1 and
2-2 are connected to the cell C1 and the terminal 2-3 is connected
to the cell C2. Since the number of the terminals connected to the
cell C1 exceeds the connection number threshold "2", the base
station device 1 selects, out of the terminals 2-1, 2-2, and 2-4
connected to the cell C1, a handover candidate which is a terminal
to be performed a handover to the cell C3 adjacent to the cell C1.
For example, the base station device 1 selects, as the handover
candidate, the terminal 2-2 which has the best reception quality in
the adjacent cell C3.
[0035] Then, as illustrated in state (2) of FIG. 2, the base
station device 1 performs a handover of the selected terminal 2-2
to the adjacent cell C3 and reduces the transmission power of the
cell C1. As the transmission power of the cell C1 is reduced,
coverage of the cell C1 shrinks.
[0036] Here, problems of the premise technique are described. The
terminal 2-3 located in a boundary between the cell C2 and the cell
C4 adjacent to the cell C2 is considered to be suitable for the
handover candidate since the terminal has higher reception quality
for the base station 3 than the terminal 2-2 located close to the
center of the cell C1. However, in the premise technique, the base
station device 1 selects a terminal connected to the cell C1 having
the excessive number of the terminals as the handover candidate.
Thus, the base station device 1 does not select the terminal 2-3
connected to the cell C2 as the handover candidate. For this
reason, in the premise technique, even when the number of terminals
connected to the cell C2 among the cells C1 and C2 managed in the
base station device 1 is not larger than the connection number
threshold "2", the base station device 1 performs the handover to
the adjacent cell and reduction of the transmission power in the
cell C1. As a result, the premise technique deteriorates signal
quality in the cell C1.
[0037] Next, configuration of the base station device 1 according
to the embodiment is described with reference to FIG. 3. FIG. 3 is
a block diagram of the base station device according to the
embodiment. The base station device 1 illustrated in FIG. 3
includes a radio communication unit 11, a scheduler 12, a call
connection unit 13, a connection number determination unit 14, a
terminal information management unit 15, a candidate terminal
selection unit 16, a connection destination controller 17, a
handover (HO) controller 18, a reception quality collection unit
19, and a transmission power controller 20.
[0038] The radio communication unit 11 is configured to manage the
multiple cells having different frequency bands and to communicate
with the multiple cells managed therein or terminals connected to
each of the multiple cells. For example, the radio communication
unit 11 transmits/receives various signals and various data to/from
the terminals connected to each of the cells C1 and C2 via an
antenna 11a. Also, for example, the radio communication unit 11
sets the radio resource allocated by the scheduling processing to
the terminal via the antenna 11a. The radio communication unit 11
corresponds to an example of "communication unit".
[0039] The scheduler 12 performs the scheduling processing of
allocating the radio resource of each of the multiple cells to the
multiple cells or the terminals connected to each of the multiple
cells. Specifically, the scheduler 12 manages the identifier
(hereinafter referred to as a "radio resource ID") for identifying
the terminal to which the radio resource is allocated when
performing the scheduling processing. Then, the scheduler 12
allocates the radio resource of each of the multiple cells to the
terminal identified by the radio resource ID. The scheduler 12
outputs the radio resource allocated by the scheduling processing
to the radio communication unit 11.
[0040] Also, upon receiving input of a connection request from an
unconnected terminal via the radio communication unit 11, the
scheduler 12 outputs the connection request to the call connection
unit 13.
[0041] The call connection unit 13 receives input of the connection
request from the scheduler 12. The call connection unit 13 connects
the unconnected terminal to a cell designated by the connection
request. Then, the call connection unit 13 detects the number of
the terminals connected to each of the multiple cells managed by
the radio communication unit and outputs the detected number of the
terminals to the connection number determination unit 14.
[0042] The connection number determination unit 14 prestores the
connection number threshold indicating the number of the terminals
connectable to each of the multiple cells managed by the radio
communication unit 11. The connection number determination unit 14
receives input of the number of the terminals connected to each of
the multiple cells from the call connection unit 13. The connection
number determination unit 14 determines whether the number of the
terminals connected to each of the multiple cells exceeds the
connection number threshold. The connection number determination
unit 14 outputs the determination result to the terminal
information management unit 15 and the candidate terminal selection
unit 16.
[0043] The terminal information management unit 15 acquires
terminal information indicating a connection capability and a
connection state from the terminal connected to each of the
multiple cells via the radio communication unit 11, and manages the
acquired terminal information for each of the terminals. Here, the
connection capability is a capability of connecting to each of the
multiple cells managed by the radio communication unit 11 and
communicating with the base station device 1 by using the radio
resource of the connected cell. The connection state is a cell
setting state used in the communication with each of the multiple
cells managed by the radio communication unit 11 and the reception
quality of the cell. The terminal information management unit 15
receives input of the determination result from the connection
number determination unit 14. Using the determination result, the
terminal information management unit 15 determines whether the
number of the multiple terminals connected to one cell among the
multiple cells managed by the radio communication unit 11 exceeds
the connection number threshold.
[0044] When the number of the terminals connected to one cell among
the multiple cells exceeds the connection number threshold, the
terminal information management unit 15 performs the following
processing. With reference to the terminal information, the
terminal information management unit 15 acquires, for each of the
terminals, terminal information indicating the connection
capability to other cells (hereinafter referred to as "other cell")
excluding the one cell (hereinafter referred to as "exceeded cell")
in which the number of the multiple terminals exceeds the
connection number threshold, and the state of connection to the
other cell. The terminal information management unit 15 outputs the
acquired terminal information to the candidate terminal selection
unit 16. The terminal information management unit 15 corresponds to
an example of a "collection unit".
[0045] The candidate terminal selection unit 16 receives input of
the terminal information from the terminal information management
unit 15. Based on the connection capability and the connection
state indicated by the terminal information, the candidate terminal
selection unit 16 selects a first candidate terminal being a
terminal to be released from the connection with the exceeded cell
out of the multiple terminals connected to the exceeded cell, and
outputs information of the selected first candidate terminal to the
connection destination controller 17. The first candidate terminal
is a first type terminal (a terminal of first type), a second type
terminal (a terminal of second type) or a third type terminal (a
terminal of third type).
[0046] The first type terminal is a terminal simultaneously
connected to the other cell and the exceeded cell subordinate to
the other cell, and includes a connection capability of
communicating with the base station device 1 by using the radio
resources of the exceeded cell and the other cell. For example, the
first type terminal is simultaneously connected to the other cell
being a primary cell (Pcell) and the exceeded cell being a
secondary cell (Scell), and includes a carrier aggregation (CA)
capability of communicating by using the radio resources of the
Pcell and Scell.
[0047] The second type terminal is a terminal connected to either
the exceeded cell or the other cell and includes the connection
capability of communicating with the base station device 1 by using
the radio resource of the connected cell. For example, the second
type terminal is connected to either the exceeded cell or the other
cell although connectable to both of the cells, and includes a
multiband capability of communicating by using the radio resource
of the connected cell.
[0048] The third type terminal is a terminal simultaneously
connected to the exceeded cell and the other cell subordinate to
the exceeded cell and includes the connection capability of
communicating with the base station device 1 by using the radio
resources of the exceeded cell and the other cell. For example, the
third type terminal is simultaneously connected to the exceeded
cell being the Pcell and the other cell being the Scell, and
includes the CA capability of communicating by using the radio
resources of the Pcell and Scell.
[0049] FIG. 4 is a diagram for illustrating selection of the first,
second or third type terminal by the candidate terminal selection
unit 16 according to the embodiment.
[0050] The candidate terminal selection unit 16 includes the
connection capability to the other cell among the multiple
terminals connected to the exceeded cell, and selects a terminal
having a good connection state with the other cell as the first
candidate terminal. Here, including the connection capability to
the other cell means including the CA capability or the multiband
capability. The good connection state with the other cell means
that a case where the other cell is used as the Pcell or the Scell
when the terminal includes the CA capability or a case where the
Scell is not used even when the reception power is enough for using
the other cell as the Scell. Moreover, the good connection state
with the other cell means that the reception power in the other
cell is higher than a predetermined value when the terminal
includes the multiband capability. In the example of FIG. 4, the
candidate terminal selection unit 16 selects the first type
terminal which includes the CA capability and uses the other cell
as the Pcell as the first candidate terminal. In another case, for
example, the candidate terminal selection unit 16 selects the
second type terminal which includes the multiband capability and
whose reception power in the other cell is higher than a
predetermined value as the first candidate terminal. Moreover, for
example, the candidate terminal selection unit 16 selects the third
type terminal which includes the CA capability and uses the other
cell as the Scell as the first candidate terminal.
[0051] Among multiple terminals connected to the exceeded cell, the
candidate terminal selection unit 16 excludes a terminal not
including the connection capability to the other cell from the
first candidate terminal. In the example of FIG. 4, the candidate
terminal selection unit 16 excludes the terminal that is connected
to the exceeded cell only and includes a single band capability of
communicating by using the radio resource of the exceeded cell,
from the first candidate terminal.
[0052] Further, among multiple terminals connected to the exceeded
cell, the candidate terminal selection unit 16 excludes a terminal
that includes a connection capability to the other cell and has a
poor connection state with the other cell from the first candidate
terminal. Here, the poor connection state with the other cell means
that, when the terminal includes the CA capability, the reception
power in the other cell is lower than a predetermined value and the
other cell is not used as the Scell. In the example of FIG. 4, the
candidate terminal selection unit 16 excludes a terminal including
the CA capability and whose other cell is not used as the Scell
from the first candidate terminal.
[0053] Description is continued by referring back to FIG. 3. The
candidate terminal selection unit 16 receives input of the
determination result from the connection number determination unit
14. After the connection destination of the first candidate
terminal is changed to the other cell by the connection destination
controller 17 described later, the candidate terminal selection
unit 16 determines, by using the determination result, whether the
number of the multiple terminals connected to the exceeded cell
exceeds the connection number threshold. When the number of the
multiple terminals connected to the exceeded cell exceeds the
connection number threshold, the candidate terminal selection unit
16 performs the following processing. That is, the candidate
terminal selection unit 16 receives, from the reception quality
collection unit 19 described later, input of reception quality
(hereinafter referred to as "adjacent cell reception quality") of a
terminal connected to each of multiple cells in a case where the
terminal connected to each of the multiple cells connects to an
adjacent cell which is the cell of another base station device
adjacent to the multiple cells. Based on the adjacent cell
reception quality, the candidate terminal selection unit 16 selects
a second candidate terminal being a terminal to be released from
the connection with the exceeded cell or the other cell out of the
multiple terminals connected to the exceeded cell and out of the
multiple terminals connected to the other cell, and outputs the
selected second candidate terminal to the connection destination
controller 17.
[0054] Here, a processing in which the candidate terminal selection
unit 16 selects the second candidate terminal is described in
detail. The candidate terminal selection unit 16 calculates the
transmission power reduction amount such that an amount of the
transmission power for communication of the radio communication
unit 11 is more reduced as the adjacent cell reception quality
becomes lower, of each of the multiple terminals connected to the
exceeded cell or the other cell. Then, the candidate terminal
selection unit 16 selects a terminal having the lowest transmission
power reduction amount as the second candidate terminal out of the
multiple terminals connected to the exceeded cell or the other
cell. The candidate terminal selection unit 16 outputs the lowest
transmission power reduction amount corresponding to the second
candidate terminal to the connection destination controller 17. The
candidate terminal selection unit 16 corresponds to an example of a
"selection unit".
[0055] The connection destination controller 17 receives input of
the first candidate terminal or the second candidate terminal from
the candidate terminal selection unit 16. Upon receiving input of
the first candidate terminal, the connection destination controller
17 changes the connection destination of the first candidate
terminal to the other cell. Meanwhile, upon receiving input of the
second candidate terminal, the connection destination controller 17
changes the connection destination of the second candidate terminal
to the adjacent cell. Hereinafter, details of changing the
connection destination of the first candidate terminal and details
of changing the connection destination of the second candidate
terminal are described in this order.
[0056] First, details of changing the connection destination of the
first candidate terminal are described. When the first candidate
terminal is the first type terminal, the connection destination
controller 17 changes the connection destination of the first
candidate terminal to the other cell by releasing the radio
resource of the exceeded cell allocated to the first candidate
terminal. Specifically, the connection destination controller 17
releases the radio resource of the exceeded cell allocated to the
first candidate terminal by causing the scheduler 12 to delete a
radio resource ID corresponding to the first candidate terminal in
the exceeded cell being the Scell. Further, the connection
destination controller 17 instructs the first candidate terminal to
stop use of the Scell.
[0057] When the first candidate terminal is the second type
terminal, the connection destination controller 17 changes the
connection destination of the first candidate terminal to the other
cell by instructing the first candidate terminal to perform a
handover from the exceeded cell to the other cell. Specifically,
the connection destination controller 17 changes the connection
destination of the first candidate terminal to the other cell by
outputting, to the HO controller 18, a handover instruction which
instructs the first candidate terminal to perform a handover of the
exceeded cell to the other cell. Note that the handover between
cells under control of the same base station device like the
handover from the exceeded cell to the other cell is also called an
Intra-eNB handover.
[0058] When the first candidate terminal is the third type
terminal, the connection destination controller 17 performs the
following processing. That is, the connection destination
controller 17 releases the radio resource of the other cell
allocated to the first candidate terminal and changes over the
radio resource of the exceeded cell allocated to the first
candidate terminal to the radio resource of the other cell, and
thereby changes the connection destination of the first candidate
terminal to the other cell. Specifically, the connection
destination controller 17 causes the scheduler 12 to delete the
radio resource ID corresponding to the first candidate terminal in
the other cell being the Scell and thereby releases the radio
resource of the other cell allocated to the first candidate
terminal. Then, the connection destination controller 17 replaces
the radio resource ID corresponding to the first candidate terminal
in the exceeded cell being the Pcell with a free radio resource ID
in the other cell and thereby changes the radio resource of the
exceeded cell allocated to the first candidate terminal to the
radio resource of the other cell. At that time, random access
processing is performed between the base station device 1 and the
first candidate terminal.
[0059] The connection destination controller 17 changes the
connection destination of the first candidate terminal to the other
cell in the order of the first type terminal, the second type
terminal and the third type terminal. Amount of the processing for
changing the connection destination of the first candidate terminal
to the other cell becomes larger in the order of the first type
terminal, the second type terminal and the third type terminal. For
this reason, the connection destination controller 17 changes the
connection destination of the first candidate terminal to the other
cell in the order of the first type terminal, the second type
terminal and the third type terminal, which is the ascending order
of the processing amount.
[0060] FIG. 5 is a diagram for illustrating an example of changing
the connection destination of the first candidate terminal when the
first candidate terminal is the first type terminal. In FIG. 5,
assume that the base station device 1 may communicate with up to
two terminals in each of the cells C1 and C2. That is, the
connection number threshold indicating the number of the terminals
connectable to each of the cells C1 and C2 is "2". Additionally, in
FIG. 5, f1 indicates the frequency band corresponding to the cell
C1, and f2 indicates the frequency band corresponding to the cell
C2. Moreover, in FIG. 5, ID is the radio resource ID, and three
radio resource IDs are defined for each of the cells. Further, in
FIG. 5, each of #1 to #3 indicates the radio resource allocated to
the terminals 2-1 to 2-3 in each of the cells. Furthermore, in FIG.
5, assume that the terminal 2-1 is the terminal having the CA
capability, and the terminals 2-2 and 2-3 are the terminals having
the single band capability.
[0061] State (1) of FIG. 5 indicates a state in which the terminal
2-3 is newly connected to the cell C1 when the terminal 2-1 is
simultaneously connected to the cell C2 being the Pcell, and the C1
being the Scell, and the terminal 2-2 is connected to the cell C1.
Since the number of the terminals connected to the cell C1 exceeds
the connection number threshold "2", the candidate terminal
selection unit 16 of the base station device 1 selects the first
candidate terminal to be released from the connection to the cell
C1 out of the terminals 2-1, 2-2, and 2-3 connected to the cell C1
which is the exceeded cell. The terminal 2-1 corresponds to the
first type terminal since the terminal 2-1 is being simultaneously
connected to the cell C2 being the Pcell and the cell C1 being the
Scell, and communicating by using the radio resources of the Pcell
and the Scell. Thus, the candidate terminal selection unit 16
selects the terminal 2-1 being the first type terminal as the first
candidate terminal.
[0062] Then, as illustrated in state (2) of FIG. 5, the base
station device 1 changes the connection destination of the terminal
2-1 by releasing the radio resource of the cell C1 allocated to the
terminal 2-1 which is the first candidate terminal. Specifically,
the connection destination controller 17 of the base station device
1 causes the scheduler 12 to delete the radio resource ID "1"
corresponding to the terminal 2-1 in the cell C1 being the Scell
and thereby releases the radio resource of the cell C1 allocated to
the terminal 2-1. Thus, the number of the terminals connected to
the cell C1 becomes not larger than the connection number threshold
"2", and thereby the connection between the terminal 2-3 and the
base station device 1 is maintained.
[0063] FIG. 6 is a diagram for illustrating an example of changing
the connection destination of the first candidate terminal when the
first candidate terminal is the second type terminal. In FIG. 6,
assume that the base station device 1 may communicate with up to
two terminals in each of the cells C1 and C2. That is, the
connection number threshold indicating the number of the terminals
connectable to each of the cells C1 and C2 is "2". Additionally, in
FIG. 6, f1 indicates the frequency band corresponding to the cell
C1, and f2 indicates the frequency band corresponding to the cell
C2. Moreover, in FIG. 6, ID is the radio resource ID, and three
radio resource IDs are defined for each of the cells. Further, in
FIG. 6, each of #1 to #3 indicates the radio resource allocated
respectively to the terminals 2-1 to 2-3 in each of the cells.
Furthermore, in FIG. 6, assume that the terminal 2-1 is the
terminal having the multiband capability, and the terminals 2-2 and
2-3 are the terminals having the single band capability.
[0064] State (1) of FIG. 6 indicates a state in which the terminal
2-3 is newly connected to the cell C1 when the terminals 2-1 and
2-2 are connected to the cell C1. Since the number of the terminals
connected to the cell C1 exceeds the connection number threshold
"2", the candidate terminal selection unit 16 of the base station
device 1 selects the first candidate terminal to be released from
the connection to the cell C1 out of the terminals 2-1, 2-2, and
2-3 connected to the cell C1 which is the exceeded cell. The
terminal 2-1 corresponds to the second type terminal since the
terminal 2-1 includes the multiband capability and whose reception
power in the cell C2 is not smaller than a predetermined value.
Thus, the candidate terminal selection unit 16 selects the terminal
2-1 being the second type terminal as the first candidate
terminal.
[0065] Then, as illustrated in state (2) of FIG. 6, the base
station device 1 changes the connection destination of the terminal
2-1 to the cell C2 by instructing the terminal 2-1 being the first
candidate terminal to perform a handover from the cell C1 to the
cell C2. Specifically, the connection destination controller 17 of
the base station device 1 changes the connection destination of the
terminal 2-1 to the cell C2 by outputting, to the HO controller 18,
a handover instruction which instructs the terminal 2-1 to perform
the handover from the cell C1 to the cell C2. When the terminal 2-1
performs the handover from the cell C1 to the cell C2, the
scheduler 12 deletes the radio resource ID "1" corresponding to the
terminal 2-1 in the cell C1 and newly allocates the radio resource
ID "4" to the terminal 2-1 in the cell C2. Thus, the number of the
terminals connected to the cell C1 becomes not larger than the
connection number threshold "2", and thereby the connection between
the terminal 2-3 and the base station device 1 is maintained.
[0066] FIG. 7 is a diagram for illustrating an example of changing
the connection destination of the first candidate terminal when the
first candidate terminal is the third type terminal. In FIG. 7,
assume that the base station device 1 may communicate with up to
two terminals in each of the cells C1 and C2. That is, the
connection number threshold indicating the number of the terminals
connectable to each of the cells C1 and C2 is "2". Additionally, in
FIG. 7, f1 indicates the frequency band corresponding to the cell
C1, and f2 indicates the frequency band corresponding to the cell
C2. Moreover, in FIG. 7, ID is the radio resource ID, and three
radio resource IDs are defined for each of the cells. Further, in
FIG. 7, each of #1 to #3 indicates the radio resource allocated
respectively to the terminals 2-1 to 2-3 in each of the cells.
Furthermore, in FIG. 7, assume that the terminal 2-1 is the
terminal having the CA capability, and the terminals 2-2 and 2-3
are the terminals having the single band capability.
[0067] State (1) of FIG. 7 indicates a state in which the terminal
2-3 is newly connected to the cell C1 when the terminal 2-1 is
simultaneously connected to the cell C1 being the Pcell, and the C2
being the Scell, and the terminal 2-2 is connected to the cell C1.
Since the number of the terminals connected to the cell C1 exceeds
the connection number threshold "2", the candidate terminal
selection unit 16 of the base station device 1 selects the first
candidate terminal to be released from the connection to the cell
C1 out of the terminals 2-1, 2-2, and 2-3 connected to the cell C1
which is the exceeded cell. The terminal 2-1 corresponds to the
third type terminal since the terminal 2-1 is being simultaneously
connected to the cell C1 being the Pcell and the cell C2 being the
Scell and communicating by using the radio resources of the Pcell
and the Scell. Thus, the candidate terminal selection unit 16
selects the terminal 2-1 being the third type terminal as the first
candidate terminal.
[0068] Then, as illustrated in state (2) of FIG. 7, the base
station device 1 releases the radio resource of the cell C2
allocated to the terminal 2-1 which is the first candidate
terminal. Specifically, the connection destination controller 17 of
the base station device 1 causes the scheduler 12 to delete the
radio resource ID "4" corresponding to the terminal 2-1 in the cell
C2 being the Scell and thereby releases the radio resource of the
cell C2 allocated to the terminal 2-1.
[0069] Then, as illustrated in state (3) of FIG. 7, the base
station device 1 changes the connection destination of the terminal
2-1 to the cell C2 by changing over the radio resource of the cell
C1 allocated to the terminal 2-1 being the first candidate terminal
to the radio resource of the cell C2. Specifically, the connection
destination controller 17 of the base station device 1 causes the
scheduler 12 to replace the radio resource ID "1" corresponding to
the terminal 2-1 in the cell C1 being the Pcell with the radio
resource ID "4" released in the cell C2. Thus, the number of the
terminals connected to the cell C1 becomes not larger than the
connection number threshold "2", and thereby the connection between
the terminal 2-3 and the base station device 1 is maintained.
[0070] Next, details of changing the connection destination of the
second candidate terminal are described. The connection destination
controller 17 receives input of the transmission power reduction
amount from the candidate terminal selection unit 16. The
connection destination controller 17 instructs the transmission
power controller 20 to reduce the transmission power of a cell to
which the second candidate terminal is connected, by the
transmission power reduction amount, and when the transmission
power is reduced, changes the connection destination of the second
candidate terminal to the adjacent cell. Specifically, the
connection destination controller 17 changes the connection
destination of the second candidate terminal to the adjacent cell
by instructing the second candidate terminal to perform a handover
from the exceeded cell or the other cell to the adjacent cell.
[0071] When changing the connection destination of the second
candidate terminal selected out of the multiple terminals connected
to the other cell to the adjacent cell, the connection destination
controller 17 again performs the processing of changing the
connection destination of the first candidate terminal to the other
cell.
[0072] FIG. 8 is a diagram for illustrating an example of changing
the connection destination of the second candidate terminal. In
FIG. 8, assume that the base station device 1 may communicate with
up to two terminals in each of the cells C1 and C2. That is, the
connection number threshold indicating the number of the terminals
connectable to each of the cells C1 and C2 is "2". In FIG. 8, the
other base station device 3 manages the cell C3 which is the
adjacent cell located adjacent to the cell C1, and another base
station device 4 manages the cell C4 which is the adjacent cell
located adjacent to the cell C2. Additionally, in FIG. 8, f1
indicates the frequency band common to the cells C1 and C3, and f2
indicates the frequency band common to the cells C2 and C4.
Moreover, in FIG. 8, ID is the radio resource ID, and three radio
resource IDs are defined for each of the cells. Further, in FIG. 8,
each of #1 to #5 indicates the radio resource allocated to the
terminals 2-1 to 2-5 in each of the cells. Furthermore, in FIG. 8,
assume that the terminal 2-2 is the terminal having the CA
capability, and the terminal 2-1 and the terminals 2-3 to 2-5 are
the terminals having the single band capability.
[0073] State (1) of FIG. 8 indicates a state in which the terminal
2-5 is newly connected to the cell C1 being the Pcell when the
terminal 2-2 is connected to the cell C1, the terminal 2-1 is
connected to the cell C1, and the terminals 2-3 and 2-4 are
connected to the C2. In state (1) of FIG. 8, the number of the
terminals connected to the cell C1 exceeds the connection number
threshold "2". Thus, the candidate terminal selection unit 16 of
the base station device 1 selects the second candidate terminal to
be released from the connection to the cell C1 or C2 out of the
multiple terminals connected to the cell C1 which is the exceeded
cell or out of the multiple terminals connected to the other
cell.
[0074] The candidate terminal selection unit 16 calculates a
transmission power reduction amount .DELTA. such that an amount of
the transmission power is more reduced as the adjacent cell
reception quality becomes lower, of each of the multiple terminals
connected to the cell C1 which is the exceeded cell and of each of
the multiple terminals connected to the cell C2 which is the other
cell. The candidate terminal selection unit 16 stores the
calculated transmission power reduction amount .DELTA. into an
internal table by associating with each of the multiple terminals
connected to the cell C1 which is the exceeded cell and each of the
multiple terminals connected to the cell C2 which is the other
cell. FIG. 9 illustrates an example of the internal table used by
the candidate terminal selection unit 16.
[0075] With reference to the inner table, the candidate terminal
selection unit 16 selects a terminal having the lowest transmission
power reduction amount .DELTA. as the second candidate terminal out
of the multiple terminals connected to the cell C1 which is the
exceeded cell and out of the multiple terminals connected to the
cell C2 which is the other cell. In the example illustrated in FIG.
9, the terminal 2-3 is a terminal having the highest adjacent cell
reception quality with respect to the adjacent cell C4 and the
transmission power reduction amount .DELTA..sub.UE3 corresponding
to the terminal 2-3 is the lowest. Thus, the candidate terminal
selection unit 16 selects the terminal 2-3 as the second candidate
terminal.
[0076] Then, as illustrated in state (1) of FIG. 8, the base
station device 1 reduces the transmission power of the cell C2 to
which the terminal 2-3 being the second candidate terminal is
connected by the transmission power reduction amount .DELTA., and
when the transmission power is reduced, changes the connection
destination of the terminal 2-3 to the cell C4 which is the
adjacent cell. Specifically, the connection destination controller
17 of the base station device 1 instructs the transmission power
controller 20 to reduce the transmission power of the cell C2 to
which the terminal 2-3 is connected by the transmission power
reduction amount .DELTA.. Then, the connection destination
controller 17 changes the connection destination of the terminal
2-3 to the cell C4 by outputting, to the HO controller 18, the
handover instruction which instructs the terminal 2-3 to perform a
handover from the cell C2 to the cell C4. When the terminal 2-3
performs the handover from the cell C2 to the cell C4, the
scheduler 12 of the base station device 1 deletes the radio
resource ID "4" in the cell C2. In the example of FIG. 8, the
connection destination controller 17 changes the connection
destination of the terminal 2-3 selected out of the multiple
terminals connected to the cell C2 which is the other cell, not out
of the multiple terminals connected to the cell C1 which is the
exceeded cell, to the cell C4 which is the adjacent cell.
Therefore, the number of the terminals connected to the cell C1
which is the exceeded cell still exceeds the connection number
threshold "2".
[0077] When changing the connection destination of the terminal 2-3
selected out of the multiple terminals connected to the cell C2 to
the cell C4 which is the adjacent cell, the base station device 1
again performs the processing of changing the connection
destination of the first candidate terminal to the other cell as
illustrated in state (2) of FIG. 8. Specifically, the candidate
terminal selection unit 16 of the base station device 1 selects the
first candidate terminal to be released from the connection to the
cell C1 out of terminals 2-1, 2-2, and 2-5 connected to the cell C1
which is the exceeded cell. Here, the terminal 2-2 corresponds to a
kind of the third type terminal which has CA capability and is
connected only to the cell C1 being the Pcell and communicating by
using the radio resources of the Pcell. Thus, the candidate
terminal selection unit 16 selects the terminal 2-2 as the first
candidate terminal. Then, the connection destination controller 17
of the base station device 1 causes the scheduler 12 to replace the
radio resource ID "2" corresponding to the terminal 2-2 in the cell
C1 which is the Pcell with the radio resource ID "4" released in
the cell C2. That is, the Pcell of the terminal 2-2 is changed from
the cell C1 to the cell C2. Thus, the number of the terminals
connected to the cell C1 becomes not larger than the connection
number threshold "2", and thereby the connection between the
terminal 2-5 and the base station device 1 is maintained.
[0078] Description is continued by referring back to FIG. 3. The HO
controller 18 performs the predetermined processing of handover
with the radio communication unit 11 in accordance with the
instruction from the connection destination controller 17.
[0079] The reception quality collection unit 19 collects adjacent
cell reception quality from the terminals connected to each of the
multiple cells managed by the radio communication unit 11. The
reception quality collection unit 19 outputs the collected adjacent
cell reception quality to the candidate terminal selection unit
16.
[0080] The transmission power controller 20 controls, for each of
the cells, transmission power which is managed in the radio
communication unit 11. For example, the transmission power
controller 20 controls the radio communication unit 11 in
accordance with the instruction from the connection destination
controller 17 and thereby reduces the transmission power of the
cell to which the second candidate terminal is connected, by the
transmission power reduction amount.
[0081] Next, an example of a process flow of changing the
connection destination of the terminal by the base station device
according to the embodiment is described with reference to FIG. 10.
FIG. 10 is a flowchart of a process of changing the connection
destination of the terminal by the base station device according to
the embodiment.
[0082] As illustrated in FIG. 10, the base station device 1 waits
if there is no connection request (No in step S101). Meanwhile,
when there is a connection request (Yes in step S101), the base
station device 1 detects whether the number of the multiple
terminals connected to one cell among the multiple cells managed by
the radio communication unit 11 exceeds the connection number
threshold (step S102). If the number of the multiple terminals
connected to one cell among the multiple cells is not larger than
the connection number threshold (No in step S102), the base station
device 1 ends the processing.
[0083] Meanwhile, if the number of the multiple terminals connected
to one cell among the multiple cells exceeds the connection number
threshold (Yes in step S102), the base station device 1 performs an
in-cell connection destination changing processing (step S103). The
in-cell connection destination changing processing is a processing
of selecting the first candidate terminal being the terminal to be
released from the connection to the exceeded cell out of the
multiple terminals connected to the exceeded cell, and changing the
connection destination of the first candidate terminal to the other
cell. Details of the in-cell connection destination changing
processing are described later. After performing the in-cell
connection destination changing processing, if the number of the
multiple terminals connected to the exceeded cell is not larger
than the connection number threshold (No in step S104), the base
station device 1 ends the processing.
[0084] If the number of the multiple terminals connected to the
exceeded cell exceeds the connection number threshold (Yes in step
S104), the base station device 1 performs an out-cell connection
destination changing processing (step S105). The out-cell
connection destination changing processing is a processing of
selecting the second candidate terminal being the terminal to be
released from the connection to the exceeded cell or the other cell
among the multiple terminals connected to the exceeded cell and the
multiple terminals connected to the other cell, and changing the
connection destination of the second candidate terminal to the
adjacent cell. Details of the out-cell connection destination
changing processing are described later.
[0085] In the out-cell connection destination changing processing,
when the connection destination of the second candidate terminal
selected out of the multiple terminals connected to the other cell
is changed to the adjacent cell (Yes in step S106), the base
station device 1 returns the processing to the step S103 and again
performs the in-cell connection destination changing
processing.
[0086] Meanwhile, in the out-cell connection destination changing
processing, when the connection destination of the second candidate
terminal selected out of the multiple terminals connected to the
exceeded cell is changed to the adjacent cell (No in step S106),
the base station device 1 ends the processing.
[0087] Next, an example of a flow of the in-cell connection
destination changing processing according to the embodiment is
described with reference to FIG. 11. FIG. 11 is a flowchart of the
in-cell connection destination changing processing according to the
embodiment. The in-cell connection destination changing processing
illustrated in FIG. 11 corresponds to the step S103 illustrated in
FIG. 10.
[0088] As illustrated in FIG. 11, the terminal information
management unit 15 of the base station device 1 recognizes the
multiple terminals connected to the exceeded cell (step S201) and
acquires, for each of the terminals, terminal information
indicating the connection capability to the other cell and the
connection state with the other cell (step S202).
[0089] Based on the connection capability and the connection state
indicated in the terminal information, the candidate terminal
selection unit 16 selects the first candidate terminal out of the
multiple terminals connected to the exceeded cell (step S203). The
first candidate terminal is the first type terminal, the second
type terminal or the third type terminal.
[0090] The connection destination controller 17 generates the
candidate terminal list with the first candidate terminals
rearranged in the order of the first type terminal, the second type
terminal and the third type terminal (step S204).
[0091] FIG. 12 is a diagram for illustrating an example of
generating the candidate terminal list. On the left side of FIG.
12, assume that out of the multiple terminals (UE1 to UE6)
connected to the exceeded cell, the terminals UE1, UE2, UE3 and UE5
are selected as the first candidate terminal based on the
connection capability and the connection state. The terminal UE1 is
the second type terminal. The terminal UE2 is the third type
terminal. The terminal UE3 is the first type terminal. The terminal
UE5 is the second type terminal and has a lower reception power in
the other cell than the terminal UE1 of the same type. In such a
case, as illustrated on the right side of FIG. 12, the connection
destination controller 17 generates the candidate terminal list by
rearranging the candidate terminals UE1, UE2, UE3, and UE5 in the
order of the first type terminal, the second type terminal and the
third type terminal.
[0092] Description is continued by referring back to FIG. 11. The
connection destination controller 17 selects one first terminal
candidate from the candidate terminal list in the order of the
first type terminal, the second type terminal and the third type
terminal (step S205).
[0093] When the selected first candidate terminal is the first type
terminal (Yes in step S206), the connection destination controller
17 changes the connection destination of the first candidate
terminal to the other cell by releasing the radio resource of the
exceeded cell allocated to the first candidate terminal (step
S207).
[0094] When the selected first candidate terminal is the second
type terminal (No in step S206 and Yes in step S208), the
connection destination controller 17 determines whether there is a
free ID in the other cell (step S208a). When there is the free ID
in the other cell (Yes in step S208a), the connection destination
controller 17 changes the connection destination of the first
candidate terminal to the other cell by instructing the first
candidate terminal to perform the handover from the exceeded cell
to the other cell (step S209). Meanwhile, when there is no free IDs
in the other cell (No in step S208a), the connection destination
controller 17 shifts the processing to the step S212a.
[0095] When the selected first candidate terminal is the third type
terminal (No in step S208), the connection destination controller
17 performs the following processing. That is, the connection
destination controller 17 releases the radio resource of the other
cell allocated to the first candidate terminal (step S210) and
changes over the radio resource of the exceeded cell allocated to
the first candidate terminal to the radio resource of the other
cell (step S211). Thus, the connection destination controller 17
changes the connection destination of the first candidate terminal
to the other cell.
[0096] Then, the connection destination controller 17 determines
whether the number of selected first candidate terminals has
reached a predetermined number (step S212a). When the number of
selected first candidate terminals reaches the predetermined number
(Yes in step S212a), the connection destination controller 17 ends
the processing.
[0097] Meanwhile, if the number of selected first candidate
terminals does not reach the predetermined number (No in step
S212a), the connection destination controller 17 shifts the
processing to the step S212.
[0098] If all first candidate terminals are not selected from the
candidate terminal list (No in step S212), the connection
destination controller 17 returns the processing to the step S205.
If all first candidate terminals are selected from the candidate
terminal list (Yes in step S212), the connection destination
controller 17 ends the processing. That is, the connection
destination controller 17 repeats the processing of steps S205 to
S212 and thereby changes the connection destination of the first
candidate terminal to the other cell in the order of the first type
terminal, the second type terminal and the third type terminal with
reference to the candidate terminal list.
[0099] Next, an example of a flow of the out-cell connection
destination changing processing according to the embodiment is
described with reference to FIG. 13. FIG. 13 is a flowchart of the
out-cell connection destination changing processing according to
the embodiment. The out-cell connection destination changing
processing illustrated in FIG. 13 corresponds to the step S105
illustrated in FIG. 10.
[0100] As illustrated in FIG. 13, the reception quality collection
unit 19 of the base station device 1 collects the adjacent cell
reception quality from the terminals connected to each of the
multiple cells managed by the radio communication unit 11 (step
S301).
[0101] The candidate terminal selection unit 16 calculates the
transmission power reduction amount such that an amount of the
transmission power used for communication of the radio
communication unit 11 is more reduced as the adjacent cell
reception quality becomes lower, of each of the multiple terminals
connected to the exceeded cell and of each of the multiple
terminals connected to the other cell (step S302).
[0102] The candidate terminal selection unit 16 selects, out of the
multiple terminals connected to the exceeded cell and the multiple
terminals connected to the other cell, a terminal having the lowest
transmission power reduction amount as the second candidate
terminal (step S303).
[0103] The connection destination controller 17 instructs the
transmission power controller 20 to reduce the transmission power
of the cell to which the second candidate terminal is connected, by
the transmission power reduction amount (step S304).
[0104] The connection destination controller 17 changes the
connection destination of the second candidate terminal to the
adjacent cell by instructing the second candidate terminal to
perform the handover from the exceeded cell or other cell to the
adjacent cell (step S305).
[0105] As described above, when the number of terminals connected
to one cell exceeds the connection number threshold, the base
station device 1 according to the embodiment selects the first
candidate terminal based on the connection capability to the other
cell excluding the exceeded cell, and based on the connection state
to the other cell, and changes the connection destination of the
selected first candidate terminal to the other cell. Thus,
according to the embodiment, the number of the terminals may be
reduced by using the other cell managed by the base station device
1 in the exceeded cell in which the number of the terminals exceeds
the connection number threshold, without performing the handover to
the adjacent cell being a cell of the other base station device and
reducing the transmission power. As a result, according to the
embodiment, deterioration of the signal quality in each of the
multiple cells managed by the base station device 1 may be
suppressed.
[0106] If the number of the terminals still exceeds the connection
number threshold after the connection destination of the first
candidate terminal is changed to the other cell, the base station
device 1 selects the second candidate terminal out of the terminals
connected to the exceeded cell and out of the terminals connected
to the other cell, and changes the connection destination of the
selected second candidate terminal to the adjacent cell. As a
result, according to the embodiment, the number of the terminals
may be reduced by using the adjacent cell of the other base station
device adjacent to a cell managed by the base station device 1, and
deterioration of the signal quantity in the cell with respect to a
terminal staying in the cell managed by the base station device 1
may be reduced.
[0107] (Hardware Configuration)
[0108] The base station device 1 of the above embodiment may be
implemented, for example, by such a hardware configuration as
illustrated in FIG. 14. FIG. 14 illustrates a hardware
configuration example of the base station device.
[0109] As illustrated in FIG. 14, the base station device 1
includes, as hardware components, a processor 1001, a memory 1002,
and a radio frequency (RF) circuit 1003. The RF circuit 1003
includes an antenna 1003a. The memory 1002 comprises, for example,
a random access memory (RAM), a read only memory (ROM), and a flash
memory. The radio communication unit 11 illustrated in FIG. 3 is
implemented, for example, by an analog circuit such as the RF
circuit 1003. The scheduler 12, the call connection unit 13, the
connection number determination unit 14, the terminal information
management unit 15, the candidate terminal selection unit 16, the
connection destination controller 17, the HO controller 18, the
reception quality collection unit 19 and the transmission power
controller 20 are implemented by an integrated circuit such as, for
example, the processor 1001.
[0110] Various processings described in the above embodiment may be
implemented when programs prepared in advance are executed by a
computer. Programs corresponding to processings performed by the
scheduler 12, the call connection unit 13, the connection number
determination unit 14, the terminal information management unit 15,
the candidate terminal selection unit 16, the connection
destination controller 17, the HO controller 18, the reception
quality collection unit 19 and the transmission power controller 20
are stored in the memory 1002. Then, each program functions as a
process when read by the processor 1001.
[0111] All examples and conditional language recited herein are
intended for pedagogical purposes to aid the reader in
understanding the invention and the concepts contributed by the
inventor to furthering the art, and are to be construed as being
without limitation to such specifically recited examples and
conditions, nor does the organization of such examples in the
specification relate to a showing of the superiority and
inferiority of the invention. Although the embodiments of the
present invention have been described in detail, it should be
understood that the various changes, substitutions, and alterations
could be made hereto without departing from the spirit and scope of
the invention.
* * * * *